Vibration sensor

ABSTRACT

The present invention relates to a vibration sensor comprising a pressure generating element for generating pressure differences between a first and a second volume in response to vibrations of the vibration sensor, the first and second volumes being acoustically sealed from each other, and a pressure transducer for measuring pressure differences between the first and second volumes. The present invention also relates to an associated method for detecting vibrations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/269,404, filed on Feb. 6, 2019, which claims priority to and thebenefit of European Application No. 18170039.4, filed Apr. 30, 2018,each of which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a vibration sensor comprising apressure transducer for measuring pressure differences between a firstand a second volume being acoustically sealed from each other. Thepressure differences between the first and second volumes are generatedby a pressure generating element in response to vibrations of thevibration sensor.

BACKGROUND OF THE INVENTION

Vibration sensors of today mostly rely on microelectromechanical systems(MEMS), i.e. MEMS based vibration sensors. However, an intrinsic andlarge drawback of traditional MEMS based vibration sensors is thelimited weight of the moveable mass as this limitation has a significantimpact on the fundamental noise floor of the vibration sensors, i.e. theJohnson-Nyquist noise level.

In order to deal with the above-mentioned noise issues an often appliedstrategy to lower the noise floor is to limit the bandwidth of thevibration sensor. However, this approach makes most MEMS based vibrationsensors incompatible with own voice pickup.

Thus, there seems to be a need for MEMS based vibration sensors havingboth an acceptable noise floor level as well as an acceptable bandwidth.

It may thus be seen as an object of embodiments of the present inventionto provide a vibration sensor having an acceptable balance between noisefloor level, bandwidth and size. It may be seen as a further object ofembodiments of the present invention to provide a vibration sensorhaving a considerably smaller volume compared to traditional vibrationsensor systems.

DESCRIPTION OF THE INVENTION

The above-mentioned object is complied with by providing, in a firstaspect, a vibration sensor comprising (i) a pressure generating elementfor generating pressure differences between a first and a second volumein response to vibrations of the vibration sensor, the first and secondvolumes being acoustically sealed from each other, and (ii) a pressuretransducer for measuring pressure differences between the first andsecond volumes.

The present invention thus relates to a vibration sensor comprising apressure generating element and a pressure transducer adapted to measurepressure differences between a first volume and a second volume. Thesepressure differences are generated by the pressure generating element inresponse to vibrations of the vibration sensor.

The pressure transducer and the pressure generating element are arrangedin parallel which is advantageous in that it eliminates the need forcompliant volumes in connection with both the pressure transducer andthe pressure generating element. With no compliant volumes the design ofthe vibration sensor can be made considerably smaller. Moreover, thesensitivity of the vibration sensor according to the present inventionmay be significantly increased by reducing the volume.

The pressure generating element and the pressure transducer may formpart of, or may be secured to, an arrangement that acoustically sealsthe first volume from the second volume. Typically, the first and secondvolumes form part of the vibration sensor.

The pressure generating element may interact directly with air of thefirst and second volumes. One possible way to comply with this mayinvolve that the pressure generating element is adjacently arrangedrelative to the first and second volumes. By adjacent is meant that thepressure generating element may form at least part of a boundary or wallthat separates the first volume from the second volume.

The pressure generating element may be implemented in various ways. Inone embodiment the pressure generating element may comprise a moveableelement operatively connected to a static element via one or moreresilient interconnections. By resilient is meant that the moveableelement seeks towards a centre position when not being exposed tovibrations. The static and moveable elements, and the one or moreresilient interconnections may form, in combination, a one piececomponent, i.e. a component being made of the same material. The one ormore resilient interconnections may form one or more hinges between thestatic element and the moveable element.

One or more openings may be provided between the static element and themoveable element so that at least part of the moveable element isallowed to move relative to the static element in response to vibrationsof the vibration sensor.

The static and moveable elements, and the one or more resilientinterconnections, may be formed by a printed circuit board (PCB) havingone or more electrically conducting paths arranged thereon. The one ormore electrically conducting paths may be adapted to guide electricalsignals to and/or from the pressure transducer and/or other electroniccircuits.

Alternatively, the static and moveable elements, and the one or moreresilient interconnections may constitute discrete components ofdifferent materials. Thus, the static element may be made of onematerial, the moveable element may be made of another material, and theone or more resilient interconnections may be made of yet anothermaterial. Also in this implementation one or more openings may beprovided between the static element and the moveable element so that atleast part of the moveable element is allowed to move relative to thestatic element in response to vibrations of the vibration sensor.

The static or movable element and/or the pressure transducer maycomprise a small hole having a predetermined resistance between thefirst and second volumes. The predetermined resistance of the small holeinduces a low-frequency roll-off. A viscoelastic substance may bearranged in the one or more openings between the static element and themoveable element so as to form an acoustic seal therebetween.

As it will be addressed in further details below the viscoelasticsubstance may have a viscosity within the range between 1000 and 100000cP, such as between 2000 and 80000 cP, such as between 3000 and 50000cP, such as between 4000 and 40000 cP, such as between 5000 and 30000cP, such as between 6000 and 20000 cP, such as around 10000 cP. Theviscoelastic substance may be an oil product in that oil is stable overtime and it does not tend to evaporate. Moreover, oil comes with a widerange of viscosities. Other suitable candidates as viscoelasticsubstances may involve gels, magnetic fluids etc.

Alternatively or in combination therewith, a foil or membrane may bearranged in the one or more openings between the static element and themoveable element so as to form the acoustic seal therebetween.

In terms of implementation various embodiments exist. In one embodimentthe pressure transducer may be secured to the moveable element.Moreover, a signal processing circuitry, such as an application specificintegrated circuit (ASIC), for processing signals from the pressuretransducer may be secured to the moveable element. Alternative, thesignal processing circuitry for processing signals from the pressuretransducer may be secured to the static element.

The ASIC may not be limited to processing signals from the pressuretransducer. It may process or generate analogue or digital signalsprovided by or send to other transducers, DSPs or ASICs.

Instead of being secured to the moveable element the pressure transducermay be secured to the static element. While the pressure transducer issecured to the static element the signal processing circuitry forprocessing signals from the pressure transducer may be secured to themoveable element. Alternatively, the signal processing circuitry forprocessing signals from the pressure transducer may be secured to thestatic element. With both the pressure transducer and the signalprocessing circuitry secured to the static element a separate mass maybe secured to the moveable element. The pressure transducer may comprisea MEMS pressure transducer. In order not increase the height of thevibration sensor the pressure transducer and the signal processingcircuitry may be arranged next to each other, such as next to each otheron a PCB forming the static and/or moveable elements.

To change the performance characteristics of the vibration sensor one ormore additional masses may be added to the moveable element in order toreduce noise. The addition of such one or more additional masses isindependent of the position of the pressure transducer and signalprocessing circuitry. The mass to spring stiffness ratio determines thesensitivity and peak frequency position of the vibration sensor.

In a second aspect the present invention relates to a personal devicecomprising a vibration sensor according to the first aspect, saidpersonal device being selected from the group consisting of hearingaids, hearing devices, hearables, mobile communication devices andtablets.

In a third aspect the present invention relates to a method fordetecting vibrations, the method comprising the steps of (i) generatingpressure differences between a first and a second volume beingacoustically sealed from each other, and (ii) measuring pressuredifferences between the first and second volumes using a pressuretransducer.

The method according to the third aspect may be performed using avibration sensor of the type disclosed in connection with the firstaspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in further details withreference to the accompanying figures, wherein

FIG. 1 shows a moveable mass system and a pressure transducer inparallel.

FIG. 2 a shows a first embodiment of the present invention.

FIG. 2 b shows the details of the static element of the first embodimentof FIG. 2 a.

FIG. 3 shows an exploded view of the first embodiment of the presentinvention.

FIG. 4 a shows an exploded view of a second embodiment of the presentinvention.

FIG. 4 b shows the details of the static element of the secondembodiment of FIG. 4 a.

FIG. 5 a shows an exploded view of a third embodiment of the presentinvention.

FIG. 5 b shows the details of the static element of the third embodimentof FIG. 5 a.

FIG. 6 shows a fourth embodiment of the present invention.

FIG. 7 shows a fifth embodiment of the present invention.

While the invention is susceptible to various modifications andalternative forms specific embodiments have been shown by way ofexamples in the drawings and will be described in details herein. Itshould be understood, however, that the invention is not intended to belimited to the particular forms disclosed. Rather, the invention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In its broadest aspect the present invention relates to a vibrationsensor comprising a pressure transducer and a pressure generatingelement arranged in parallel. The pressure transducer is adapted tomeasure pressure differences between a first volume and a second volume.These pressure differences are generated by the pressure generatingelement in response to vibrations of the vibration sensor.

The parallel arrangement of the pressure transducer and the pressuregenerating element is advantageous in that it eliminates the need for acompliant volume in connection with both the pressure transducer and thepressure generating element whereby the design of the vibration sensorcan be made considerably smaller. Moreover, the sensitivity of thevibration sensor according to the present invention may be significantlyincreased.

With reference to FIG. 1 the general principle of the present inventionis depicted in the form of a vibration sensor 100 having a pressuretransducer 107 and a pressure generating element 103 arranged inparallel. At least part of the pressure generating element 103 isadapted to move and/or bend as indicated by the arrow 104 when thevibration sensor is exposed to vibrations. The moving and/or bending ofat least part of the pressure generating element 103 introduces pressuredifferences between the first volume 101 and the second volume 102 whichare acoustically sealed from each other. The pressure transducer 107,which in FIG. 1 is secured to a static element 105 having athrough-going opening 106, is adapted to measure the generated pressuredifferences between the first volume 101 and the second volume 102.

As seen in FIG. 1 the pressure generating element 103 interacts directlywith air of the first 101 and second 102 volumes in that the pressuregenerating element 103 is adjacently arranged relative to the first 101and second 102 volumes, i.e. the pressure generating element 103 formsat least part of a boundary or wall that separates the first volume 101from the second volume 102. The dimensions of the first 101 and second102 volumes should be kept as small as possible. Moreover, thecompliance of the pressure transducer 107 should also be kept at aminimum although still suitable for sensing pressure variations.Finally, the surface of the pressure generating element should be aslarge as possible in order to secure proper acoustical amplification.

Thus, according to the present invention a pressure generating element103 for generating pressure differences, and a pressure transducer 107for detecting said pressure differences are arranged in parallel withina vibration sensor 100. It should be noted that the pressure transducer107 and/or a signal processing circuitry electrically connected theretomay form part of the pressure generating element 103 as it will bedemonstrated in the embodiments illustrated below.

An embodiment of a vibration sensor according to the present inventionis depicted in FIGS. 2 and 3 . Referring now to FIG. 2 a a pressuregenerating element comprising a moveable element 202, a pressuretransducer 204 and a signal processing circuitry 205 for processingsignals from the pressure transducer 204 are depicted. The pressuretransducer 204 applied in the embodiment shown in FIG. 2 a is MEMSmicrophone. In the embodiment shown in FIG. 2 a the moveable element202, the pressure transducer 204 and the signal processing circuitry 205thus constitute, in combination, a moveable mass system being adapted togenerate pressure differences.

The pressure transducer 204 and the signal processing circuitry 205 areelectrically connected via an appropriate number of wires 206 which maydiffer from the two wires shown in FIG. 2 a . The pressure generatingelement in the form of the moveable element 202, a pressure transducer204 and a signal processing circuitry 205 are moveably arranged relativeto the static element 201 in that one or more openings 203 are providedbetween the static element 201 and the moveable element 202. Anappropriate number of resilient interconnections or hinges 211, 212, 213are provided between the static element 201 and the moveable element202.

In the embodiment shown in FIG. 2 a the moveable element 202, the staticelement 201 and the resilient interconnections or hinges 211, 212, 213form a one piece component in the form of a PCB having electricallyconducting PCB tracks 208, 209, 210 arranged thereon. The PCB tracks208, 209, 210 ensure that electrical signals may be provided to and/orfrom the signal processing circuitry 205, i.e. across the resilientinterconnections or hinges 211, 212, 213. The signal processingcircuitry 205 is electrically connected to the PCB tracks 208, 209, 210via an appropriate number of wires 207 which may differ from the threewires shown in FIG. 2 a . Alternatively, the signal processing circuitry205 may be electrically connected to the PCB tracks 208, 209, 210 as asurface mounted device (SMD). Similarly, the pressure transducer 204 maybe an SMD.

As it will be explained in connection with FIG. 3 the first and secondvolumes discussed in connection with FIG. 1 will be above and below thearrangement shown in FIG. 2 a , respectively. In order to form anacoustic seal between the first and second volumes a viscoelasticsubstance is arranged in the one or more openings 203 between the staticelement 201 and the moveable element 202.

It should be noted that if the one or more openings 203 between thestatic element 201 and the moveable element 202 is/are small enough theresistance of the one or more openings 203 increase to the order ofmagnitude of a regular compensation hole. Thus, if the one or moreopenings 203 is/are small enough the one or more openings 203 willfunction as one or more compensation holes and thus introduce additionallow-frequency roll-off. In this implementation no additional sealingmeasure is needed.

The viscoelastic substance may have a viscosity within the range between1000 and 100000 cP, such as between 2000 and 80000 cP, such as between3000 and 50000 cP, such as between 4000 and 40000 cP, such as between5000 and 30000 cP, such as between 6000 and 20000 cP, such as around10000 cP. A suitable candidate as a viscoelastic substance may involveoil in that oil is stable over time and it does not tend to evaporate.Moreover, oil comes with a wide range of viscosities. Other suitablecandidates as viscoelastic substances may involve gels, magnetic fluidsetc.

The PCB forming the static element 214, the moveable element 215 and theintegrated resilient interconnections or hinges 218 are shown in greaterdetails in FIG. 2 b . Similar to FIG. 2 a PCB tracks 219 are arrangedacross the respective resilient interconnections or hinges 218 thatinterconnect the static element 214 and the moveable element 215. EachPCB track 219 terminates in a track pad 220 which facilitates furtherelectrical connections. As addressed above one or more openings 216 areprovided between the static element 214 and the moveable element 215 sothat the moveable element 215 may move relative to the static element214. Moreover, a viscoelastic substance is arranged in these one or moreopenings 216 in order to form an acoustic seal between the first andsecond volumes. As previously addressed the pressure transducer 204, cf.FIG. 2 a , is adapted to detect pressure differences between the firstand second volumes. In order to do this an acoustical opening 217 isprovided in the moveable element 215, cf. FIG. 2 b.

Referring now to FIG. 3 an embodiment of a complete vibration sensor 300is depicted. The pressure generating element involving the moveableelement 202, a pressure transducer 204 and a signal processing circuitry205 for processing signals from the pressure transducer 204, cf. FIG. 2a , are denoted 305 in FIG. 3 . As seen in FIG. 3 a spacer 303 isarranged between the assembly 305 and the connection plate 301—thelatter having an appropriate number of electrical contact zones 302 thatare electrically connected to the contact pads of the assembly 305 viaconnectors 304 in the spacer 303. As addressed above the pressuretransducer of the assembly 305 is adapted to detect pressure differencesbetween a first volume and a second volume. In FIG. 3 the first volumeis provided by cavity 308 in the spacer 303, whereas the second volumeis provided by the cavity 309 in the spacer 306 which is arrangedbetween the assembly 305 and the top plate 307. Thus, in the vibrationsensor shown in FIG. 3 the assembly 305 comprising the moveable element,the pressure transducer and the signal processing circuitry forprocessing signals from the pressure transducer are arranged between thefirst and second volumes being defined by cavities 308, 309.

Another embodiment of a vibration sensor 400 according to the presentinvention is depicted in FIG. 4 . The vibration sensor 400 shown in FIG.4 a comprises a housing 412, a spacer 411 and a cover plate 401 havingan appropriate number of electrical connections 403 arranged on anon-conducting plate 402. Moreover, an assembly comprising a staticelement 404, 405 and a moveable element 406 having a pressure transducer409 secured thereto. The moveable element 406 and the pressuretransducer 409 thus constitute a moveable mass system in combination,whereas the signal processing circuitry 408 for processing signals fromthe pressure transducer 409 is secured to the static element 404. Themoveable element 406 is connected to the static element 404 via anappropriate number of resilient interconnections or hinges 410.Moreover, one or more openings 407 are provided between the moveableelement 406 and the static element 404, 405 so that the moveable element406 is allowed to move relative to the static element 404, 405. Similarto the embodiment shown in FIGS. 2 and 3 a viscoelastic substance isarranged in the one or more openings 407 in order to form an acousticseal between a first volume being defined above the assembly of thestatic element 404, 405 and the moveable element 406, and a secondvolume being defined by a cavity in the spacer 411.

FIG. 4 b shows a more detailed view of the static element 413, 418, themoveable element 414, the one or more resilient interconnections orhinges 417 and the one or more openings 415. An acoustical opening 416is provided in the moveable element 414 so that a pressure transducer(not shown) secured thereto is allowed to detect pressure differencesbetween the first and second volumes. As addressed above a viscoelasticsubstance is arranged in the one or more openings 415 in order to forman acoustic seal between the first and second volumes. The staticelement 413, 418, the moveable element 414, and the one or moreresilient interconnections or hinges 417 may be implemented as a onepiece component, or they may be assembled using different materials,such as one material for the static element 413, 418, another materialfor the moveable element 414, and a third material for the one or moreresilient interconnections or hinges 417.

Referring now to FIG. 5 , yet another embodiment 500 of the vibrationsensor of the present invention is depicted. Compared to the embodimentshown in FIG. 4 the pressure transducer 508 is now secured to the staticelement 504, 505, whereas the signal processing circuitry 509constitutes a moveable mass system together with the moveable element506 which is connected to the static element 504 via one or moreresilient interconnections or hinges 510. A viscoelastic substance isprovided in the one or more openings 507 in order to form an acousticseal between a first volume being defined above the assembly of thestatic element 504, 505 and the moveable element 506, and a secondvolume being defined by a cavity in the spacer 511. The vibration sensor500 further comprises a housing 512, a spacer 511 and a cover plate 501having an appropriate number of electrical connections 503 arranged on anon-conducting plate 502.

FIG. 5 b shows a more detailed view of the static element 513, 514, themoveable element 515, the one or more resilient interconnections orhinges 517 and the one or more openings 516. An acoustical opening 518is provided in the static element 518 so that a pressure transducer (notshown) secured thereto is allowed to detect pressure differences betweenthe first and second volumes within the housing 512. As alreadydiscussed a viscoelastic substance is arranged in the one or moreopenings 516 in order to form an acoustic seal between the first andsecond volumes. Similar to the embodiment shown in FIG. 4 the staticelement 513, 514, the moveable element 515, and the one or moreresilient interconnections or hinges 517 may be implemented as a onepiece component, or they may be assembled using different materials,such as one material for the static element 513, 514 another materialfor the moveable element 515, and a third material for the one or moreresilient interconnections or hinges 517.

As depicted in FIGS. 2-5 pressure transducers 204, 409, 508 and theassociated signal processing circuitries 205, 408, 509 are arranged nextto each other, i.e. on the same level, in order not to increase theheight of the vibration sensor.

FIG. 6 shows yet another embodiment 600 of the present invention whereina moveable mass system is suspended between a first volume 601 and asecond volume 602 using suspension elements 607, 608. The moveable masssystem comprises a moveable element 606 onto which a MEMS pressuretransducer is secured. The moveable element 606 and the MEMS pressuretransducer thus form, in combination, a pressure generating elementwhich is capable of moving as indicated by the arrow 609 in response tovibrations of the vibration sensor. The MEMS pressure transducer is inthe form of a MEMS microphone comprises a moveable diaphragm 605 beingcapable of detecting pressure differences between the first and secondvolumes 601, 602. Moreover, a third volume 603 and a high compliantmoveable diaphragm 604 are provided.

FIG. 7 shows another embodiment of a vibration sensor 700 comprising aMEMS microphone and a pressure generator arranged on top of the MEMSmicrophone. The MEMS microphone may apply various technologies,including piezo, charged plate capacitor etc. The signal processing ofthe MEMS microphone may be analog or digital applying any digital codingscheme.

The MEMS microphone comprises a housing having a top PCB 702 and abottom PCB 703 on which electrodes 716, 717 for electrically connectingthe vibration sensor 700 are provided. The electrodes 716, 717 may be inthe form of solder pads.

An acoustical opening 710 is provided in the top PCB 702. A wall portion701 is provided between the top PCB 702 and the bottom PCB 703. Withinthe MEMS microphone a MEMS cartridge 711 comprising a membrane 712 and afront chamber 718 is provided. The MEMS microphone further comprises aback chamber 714 within which back chamber 714 a signal processorcircuitry 713 and one or more via's 715 are provided. As addressed abovea pressure generator is arranged on top of the MEMS microphone. As seenin FIG. 7 the pressure generator is secured to the top PCB 702. Thepressure generator comprises a housing 704, a pressure generatingelement 706 and a moveable mass 705 secured to the pressure generatingelement 706. The pressure generating element 706 and the moveable mass705 comprise respective acoustical openings 708 and 707.

The housing 704 of the pressure generator can be made of any suitablematerial as long as it seals the inside completely. Preferably, a thinmetal shield is applied. A small hole introducing a low-frequency rolloff below 10 Hz may be allowed as such a small hole does not introducedominant acoustic noise.

The mass of the moveable mass 705 is preferable around 4 mg. It isestimated that the practical minimum mass would be around 0.004 mg asthis would add +30 dB to the noise. Similarly, a mass of 0.04 mg wouldadd +20 dB to the noise, and a mass of 0.4 mg would add +10 dB to thenoise. Thus, the higher the mass of the moveable mass the lower is theeffect of the thermal movement noise of the vibration sensor.

The area of the pressure generating element 706 and the moveable mass705 should be as large as possible, and preferably larger than 0.5 mm²,such as larger than 1 mm², such as larger than 2 mm², such as largerthan 4 mm², such as larger than 6 mm², such as larger than 8 mm², suchas larger than 10 mm². A large area of the pressure generating element706 and the moveable mass 705 is advantageous as this requires a smalleramplitude of the movement of the moveable mass 705 in order to reachcertain volume displacement and thereby sensitivity.

As seen in FIG. 7 , a small volume 709 exists between the pressuregenerating element 706 and the upper side of the top PCB 702. The volumeshould be as small as possible, and preferably smaller than 5 mm³, suchas smaller than 2 mm³, such as smaller than 1 mm³, such as smaller than0.75 mm³, such as smaller than 0.5 mm³, such as smaller than 0.25 mm³,such as smaller than 0.1 mm³.

A compliant sealing 719 in the form of for example a foil, membrane,viscoelastic substance or gel is preferably provided along the edges ofthe pressure generating element 706. Preferably, the compliant sealingshould have a low stiffness and it should be able to withstand reflowtemperatures.

The volume 720 above the pressure generating element 706 and themoveable mass 705 is acoustically connected to the back volume 714 ofthe MEMS microphone via the channel or tube 721.

The invention claimed is:
 1. A vibration sensor comprising: a pressuregenerating element for generating pressure differences between a firstvolume and a second volume in response to vibrations of the vibrationsensor, the first and second volumes being acoustically sealed from eachother, wherein the pressure generating element includes a moveableelement that is configured to interact directly with air of the firstand second volumes; and a pressure transducer for measuring pressuredifferences between the first and second volumes, wherein the pressuretransducer and the pressure generating element are arranged in parallelrelative to the first and second volumes, wherein the pressuregenerating element and the pressure transducer are arranged adjacent toeach other such that the pressure generating element and the pressuretransducer are directly exposed to portions of the first and secondvolumes.
 2. A vibration sensor according to claim 1, wherein thevibration sensor further comprises a static element, the static elementbeing operatively connected to the moveable element of the pressuregenerating element via one or more resilient interconnections.
 3. Avibration sensor according to claim 2, wherein the static and moveableelements, and the one or more resilient interconnections form, incombination, a one piece component, and wherein one or more openings areprovided between the static element and the moveable element.
 4. Avibration sensor according to claim 3, wherein the static and moveableelements, and the one or more resilient interconnections, are formed bya printed circuit board having one or more electrically conducting pathsarranged thereon.
 5. A vibration sensor according to claim 3, wherein aviscoelastic substance is arranged in the one or more openings betweenthe static element and the moveable element so as to form an acousticseal therebetween.
 6. A vibration sensor according to claim 2, whereinthe static and moveable elements, and the one or more resilientinterconnections constitute discrete components of different materials,and wherein one or more openings are provided between the static elementand the moveable element.
 7. A vibration sensor according to claim 2,wherein the pressure transducer is secured to the moveable element orthe static element.
 8. A vibration sensor according to claim 7, whereina signal processing circuitry for processing signals from the pressuretransducer is secured to the moveable element or the static element. 9.A vibration sensor according to claim 8, wherein the pressure transducerand the signal processing circuitry are arranged next to each other. 10.A vibration sensor according to claim 1, wherein the pressure transducercomprises a MEMS pressure transducer.
 11. A vibration sensor accordingto claim 1, wherein the vibration sensor is contained within a personaldevice selected from the group consisting of hearing aids, hearingdevices, hearables, mobile communication devices and tablets.
 12. Avibration sensor comprising: a pressure generating element forgenerating pressure differences between a first volume and a secondvolume in response to vibrations of the vibration sensor, the first andsecond volumes being acoustically sealed from each other; and a pressuretransducer for measuring pressure differences between the first andsecond volumes, wherein the pressure transducer and the pressuregenerating element are arranged in parallel relative to the first andsecond volumes, wherein the pressure generating element and the pressuretransducer form part of an arrangement that acoustically seals the firstvolume from the second volume.
 13. A vibration sensor comprising: apressure generating element for generating pressure differences betweena first volume and a second volume in response to vibrations of thevibration sensor, the first and second volumes being acoustically sealedfrom each other; and a pressure transducer for measuring pressuredifferences between the first and second volumes, wherein both of thepressure transducer and the pressure generating element are directlyfluidically connected to the first and second volumes.
 14. A vibrationsensor according to claim 13, wherein the pressure generating elementmoves or bends in response to the vibrations of the vibration sensor togenerate the pressure differences between the first volume and thesecond volume.
 15. A vibration sensor according to claim 13, wherein thepressure generating element directly interacts with air of the first andsecond volumes.
 16. A method for detecting vibrations in a device havinga pressure generating element and a pressure transducer that are bothdirectly fluidically connected to a first volume and a second volume,the first volume and the second volume being acoustically sealed fromeach other, the method comprising: causing, by movement of the pressuregenerating element in response to the vibrations, pressure differencesbetween the first volume and the second volume; and measuring, via thepressure transducer, the pressure differences between the first volumeand the second volume.
 17. A method according to claim 16, wherein thepressure generating element is adapted to interact directly with air ofthe first and second volumes.
 18. A method according to claim 16,wherein the causing comprises: in response to the vibrations, moving atleast a part of the pressure generating element toward the first volumeand away from the second volume.
 19. A vibration sensor comprising: apressure generating element for generating pressure differences betweena first volume and a second volume in response to vibrations of thevibration sensor, the first and second volumes being acoustically sealedfrom each other; a pressure transducer for measuring pressuredifferences between the first and second volumes, wherein the pressuretransducer and the pressure generating element are arranged in parallelrelative to the first and second volumes; and a static element, thestatic element being operatively connected to a moveable element of thepressure generating element via one or more resilient interconnections;wherein the static and moveable elements, and the one or more resilientinterconnections form, in combination, a one piece component, andwherein one or more openings are provided between the static element andthe moveable element; and wherein the static and moveable elements, andthe one or more resilient interconnections, are formed by a printedcircuit board having one or more electrically conducting paths arrangedthereon.
 20. A vibration sensor comprising: a pressure generatingelement for generating pressure differences between a first volume and asecond volume in response to vibrations of the vibration sensor, thefirst and second volumes being acoustically sealed from each other; apressure transducer for measuring pressure differences between the firstand second volumes, wherein the pressure transducer and the pressuregenerating element are arranged in parallel relative to the first andsecond volumes; and a static element, the static element beingoperatively connected to a moveable element of the pressure generatingelement via one or more resilient interconnections; wherein the staticand moveable elements, and the one or more resilient interconnectionsform, in combination, a one piece component, and wherein one or moreopenings are provided between the static element and the moveableelement; and wherein a viscoelastic substance is arranged in the one ormore openings between the static element and the moveable element so asto form an acoustic seal therebetween.
 21. A vibration sensorcomprising: a pressure generating element for generating pressuredifferences between a first volume and a second volume in response tovibrations of the vibration sensor, the first and second volumes beingacoustically sealed from each other; a pressure transducer for measuringpressure differences between the first and second volumes, wherein thepressure transducer and the pressure generating element are arranged inparallel relative to the first and second volumes; and a static element,the static element being operatively connected to a moveable element ofthe pressure generating element via one or more resilientinterconnections; wherein the static and moveable elements, and the oneor more resilient interconnections constitute discrete components ofdifferent materials, and wherein one or more openings are providedbetween the static element and the moveable element.
 22. A vibrationsensor comprising: a pressure generating element for generating pressuredifferences between a first volume and a second volume in response tovibrations of the vibration sensor, the first and second volumes beingacoustically sealed from each other; a pressure transducer for measuringpressure differences between the first and second volumes, wherein thepressure transducer and the pressure generating element are arranged inparallel relative to the first and second volumes; and a static element,the static element being operatively connected to a moveable element ofthe pressure generating element via one or more resilientinterconnections; wherein the pressure transducer is secured to themoveable element or the static element; and wherein a signal processingcircuitry for processing signals from the pressure transducer is securedto the moveable element or the static element.
 23. A vibration sensoraccording to claim 22, wherein the pressure transducer and the signalprocessing circuitry are arranged next to each other.